You may have heard the saying, “failing to plan is planning to fail.” I can certainly attest to the wisdom of this, having received, shall we say… less than desirable results after neglecting to adequately prepare. This saying has been attributed to the great inventor and innovator, Benjamin Franklin. However, it is more widely accepted that Alan Lakein, the author of several books on time management, developed this quote. The debate over the true originator may never be settled, but there is an even more definitive quote on time management by Mr. Lakein: “Planning is bringing the future into the present so that you can do something about it now.”
When designing PCBs, bringing the future into the present is critical to ensuring your board can be successfully assembled, prototyped and produced. By planning ahead, you can reduce the production cycle, minimize development costs and ensure a smooth transition from the prototyping to production phases of product development. The institution of specific steps that target the assembly process into a PCB development DFM regimen is known as design for assembly (DFA). But before laying out guidelines that constitute good DFA, let’s take a look at why it’s important for PCB product development.
What Is DFA and Why Is It Important?
PCB manufacturing includes fabrication, component sourcing & acquisition and assembly. Of the three, assembly is typically the most time-consuming and expensive process. The primary objective of PCB assembly is to securely attach the correct components to the fabricated PCB. Good DFA, therefore, incorporates steps into the design process that support and enhance the PCB assembler’s ability to meet this primary objective.
In PCB product design and development, there are two assembly stages: PCB prototype assembly and PCB production assembly. Both of these should be included as part of DFA during PCB design.
PCB Prototype Assembly
The assembly process for prototyping strives to ensure the correct components are securely attached and clearance and tolerance restrictions are adhered to. DFA questions that should be asked during design include:
- Do components match their pads?
- Are components adequately spaced from each other?
- Are component markings and identification accurate and clear?
- Are drill hole rules applied?
- Are solder mask guidelines applied?
- Is thermal relief adequate?
- Are board edge clearance rules applied?
PCB Production Assembly
All of the above considerations for PCB prototype assembly apply to PCB production assembly, as well. However, we also have to take into account high volume production, testability and component availability & reliability. To aid the process, the following DFA questions need to be asked:
- Does board shape allow for panelization?
- What type of quality control testing should be used?
- Will components be readily available for future runs?
- Are thermal relief options included?
- Will the board be subjected to vibration?
Successfully addressing these questions, whether for PCB prototype or production assembly, ensures that your DFA efforts are enhancing your manufacturer’s ability to meet the primary objective: securely attaching your components in order for your board to meet its performance objectives in its intended environment. Nearly as important to your PCB design and development process is the speed at which you get your boards back from the manufacturer. Thus, the secondary objective of DFA is to institute actions during design that aid your manufacturer in performing their role as quickly and efficiently as possible.
How Does DFA Impact PCB Design and Development?
When applying DFA during the design process, the most important question to ask yourself is “How will this decision impact the assembly of my PCB?” If your decision makes the process harder, longer or more expensive, then you should reconsider. Below are some specific DFA actions that you can take, and why these actions are important. Taking these steps can ensure the above questions will be answered and the DFA solutions can be implemented within your design. Following these guidelines will assist your manufacturer in efficiently producing your boards with securely connected components to meet your design and development needs.
Although this list is not exhaustive, it is a good starting point for a smoother PCB assembly process. You might encounter additional issues if your design requires special single source components or your board placement dictates using a specific shape. As size, spacing and clearance tolerances are highly dependent on the equipment and processes used, you should include your PCB manufacturer early in the process to ensure that proper specifications are instituted. Following these specifics and maintaining clear communication with your manufacturer throughout the process is a part of good DFA implementation.
|Applying good DFM for your PCB design is more than just following rules and guidelines to simplify your board fabrication process.
Good DFM includes instituting good practices that support board assembly as well, and DFA should be an important part of your overall DFM strategy.
If you neglect to apply DFA as part of your PCB design, you may be setting yourself up for future problems with board assembly, such as longer production cycles, increased costs and unexpected hiccups when converting from prototyping to production. Prepare your board for a successful future by applying DFA before sending it off for manufacturing.
At Tempo, we work with you to simplify the process of incorporating good DFA. We furnish accurate information for your DFM, employ state-of-the-art component validation software and enable you to view and download DRC files. Additionally, if you’re an Altium user, you can easily add these files to your PCB design software.
If you’re ready to proceed and have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on DFA, DFM or how to apply best practices into your design, contact us.